1. Field of the Invention
The invention relates to portable gyroscopic compass devices of the kind adapted for surveying purposes and more particularly relates to portable gyrocompass surveying devices including means for rapidly aligning the reference device with respect to geographic north.
2. Description of the Prior Art
The accuracy of prior art gyrocompass devices and their capability of rapid alignment with the northly direction has been discussed, for example, in the W. G. Wing U.S. Pat. application Ser. No. 621,907, filed Oct. 14, 1975, entitled "Portable Surveying Gyrocompass Apparatus," and assigned to Sperry Rand Corporation, which application discloses an improvement over the prior art affording greatly enhanced rapid alignment and accuracy capabilities. The present invention represents a significant improvement over the apparatus of the prior Wing application which issued as U.S. Pat. No. 4,033,045 July 5, 1977.
IT IS THE OBJECTIVE OF THE PRIOR Wing application to provide a miniature automatically self-aligning azimuth reference that employs a floated pendulous gyrocompass device for the rapid determination of geographic north. Fast alignment with north from an initially misaligned condition is effected in an iterative manner by a vertical axis magnetic torquer-pick off system cooperating with a dual servo loop control for the rapid orientation of the system.
The floated sensitive element is pendulous, permitting the azimuth motion of the float to be controlled by the vertical axis torquer rather than by a horizontal axis torquer. The torque supplied by the vertical axis torquer is proportional to the rate of rotation of the floated sensitive element about the horizontal axis normal to the spin axis; thus, under the condition that there is no rotation of the sensitive element about this axis with respect to the vertical, the applied torque is a measure of the spin axis angle departure from north and is used in the determination of the drive angle required to reduce the northerly pointing error. The combination of elements is enclosed in a follow-up housing, servo driven about the vertical axis. The follow-up housing is successively driven in azimuth during the north-finding operation so as to become the reference for the measurement of bearing angles with respect to geographical north.
The prior Wing invention retains important advantages of its prior art while offering significant additional advantages; it retains the advantages of total absence of mechanical or electrical connections to the floated sensitive element for providing high accuracy and floatation in a free-surface liquid in a self-compensating arrangement requiring no temperature or related controls. Settling on geographic north is greatly improved as to accuracy and the time required to achieve settling. A relatively crude initial north alignment is acceptable, and local latitude does not have to be precisely known. Because the basic operation of the system is automatic, the operator needs little skill and can be trained in a short time to achieve accurate results.